1

First of all, yes, Bali is an overcrowded tourist spot, but if this is your first time visiting Indonesia, visiting Bali is a must. If only you have lots of time, I suggest you to do the islands hopping. You can visit lot of places with minimum budget. Just travel by bus or train from KL to Johor Bahru or Singapore. From both of the places you can travel by ferry to Batam island. From Batam you can find a cheap flight to Medan (south sumatera provinces) to see Lake Toba and other tourist spots. From there you just going south and visiting several cities and places along the way. Travel by bus is easy to do. From the southern most of the sumatera island, you can travel by ferry to Java island and from there you can go to the east, visiting Jakarta, Bandung, Yogyakarta, Mount Merapi, Solo, Malang, Surabaya, Mount Bromo, Banyuwangi and finally at the eastern most of Java island, you can continue your travel by ferry to Bali.
But if you only have no more than just a week, with minimum budget, I suggest you to stick around in Bali. It's a big island with lots of wonderful places to see from the sunny beaches to the mountain's view. Beside, you can easily find people who can speak english. It will help a lot for a first timer like you. There are lot of cheap motel in Bali especially around Kuta and Legian. Try the Poppies 2 road. Lots of cheap motel room there. If you still have more time, rather than visiting east java, maybe you can consider to visit Lombok island. Easier to reach from Bali.

2

Thanks a lot? What about cost of the buses? Ferry?

3

The cost may vary for every buses and ferry. Depends on the places and distance. I don't have any info about the exact price, but for the buses, it may be between US$5 - US$30 depends on the distance and the type of the buses.
For the ferry it may be between US$10 up to US$25.
The available transport by ferry as far as I know
Singapore - Batam. Apprx. 1 hours
Johor Bahru - Batam. Apprx. 1.5 hours
Bakauheni (Southern Sumatra) - Merak (Western Java). Apprx. 1.5 hours
Ketapang (Eastern Java) - Gilimanuk (Western Bali). Apprx. 1 hours

4

Thanks Few more questions
What is worth to see in Bali ?
More mountains and temple person even one day of scuba diving one day .?

5

There is so much more to Bali than Kuta and Ubud. (Though I'd take Ubud 9 days out of 10 over Kuta -- so there's my bias).

Heading east along the south coast, not far north of Candidasa is the traditional village of Tenganan -- you might find it interesting, though I haven't been there in over 10 years, so it might be entirely commercial by now. In the same general area, you can heck out Tirtaganga to combine your interest in temples and mountains --you'll find awesome rice paddies in the area. It's very beautiful: easy to google, easy access.

For mountains, you can watch sunrise from the peak of Gunung Batur and possibly cook your breakfast in the superheated ground near an active vent. On the way, the little stop at Penelokan on the rim might give you an opportunity to meet some of the worst of the Indonesian character, but persevering can give you quite an adventure -- if you stay down at a lakeside village and use that as a stepping off point for a walk up the mountain for that sunrise.

While there, a visit to the village at the far end of the lake where they leave their dead lying on the ground to dessicate will give you an insight into the original culture of Bali -- in some ways it reminded me of a film by Fellini.

I think your pace is WAY too fast, though, to se anything other than transportation: if you want to spend that much time on the road, why not just rent a bus for a week and sit in it? Seriously, 21 days is about right to get a good sense of a smaller island like Bali, perhaps -- if you want to force the pace -- with a week in Lombok.

I don't want to sound patronizing, but as a first timer, I think your biggest mistake here is trying to cover too much ground in too little time.

6

I'm agree with what north_boy said. Don't try to visit too much places in such a short periodic time. You'll get exhausted and most of your time will spend mostly on roads.
Mountain, temples, scuba diving, beaches. You name it. Everything are there in Bali. But for the two biggest temples in Indonesia (Borobudur & Prambanan), they are located near Yogyakarta, Central Java. Mount Merapi is also there. Another tourist spot.